Here are some of the latest health and medical news developments, compiled by the editors of HealthDay:

Remove Tuna From School Lunchrooms: Coalition

Tuna should be taken out of U.S. school lunchrooms, a coalition of consumer groups said after the release Wednesday of a report on mercury levels in the fish.

The call for the U.S. Department of Agriculture to take action comes after tests of tuna sold to schools found highly variable levels of mercury. In some cases, mercury levels exceeded federal guidelines, USA Today reported.

The tests on 59 samples of tuna in institutional-sized cans and foil pouches from 11 states was conduced by the non-profit Mercury Policy Project of Montpelier, Vt. In general, levels of methylmercury in the tuna were close to previous tests done by the Food and Drug Administration.

However, average methylmercury levels ranged from 0.02 to 0.64 parts per million in light tuna and between 0.19 and 1.27 parts per million in albacore tuna, USA Today reported.

"On any given day in a given school, children eating the same meal could get mercury doses that vary by tenfold," due to this variability, said report author Edward Groth. The report was sponsored by several groups, including the Center for Science in the Public Interest and Physicians for Social Responsibility.

Methylmercury is a potent neurotoxin and even tiny levels of the chemical have been linked to learning disabilities and developmental delays in children, according to U.S. Environmental Protection Agency scientists.

Canned tuna is safe and wholesome, industry groups insist. The real public health issue is that "we don't eat enough" seafood, Gavin Gibbons, of the seafood industry group the National Fisheries Institute, told USA Today.

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Many Discarded Kidneys Could Be Transplanted: Experts

In each of the last five years, more than 2,600 kidneys recovered from deceased donors in the United States were discarded without being transplanted, according to federal government data.

This occurred despite the huge number of people waiting for deceased donor kidneys. As of Wednesday, that wait list was 93,413, The New York Times reported.

Last year, 2,644 (nearly 18 percent) of the 14,784 kidneys recovered from deceased donors were discarded, according to the United Network for Organ Sharing. Nearly 500 of those kidney were not transplanted because a recipient could not be found.

The unused kidneys typically ended up in a research laboratory or medical waste incinerator. In many cases, the kidneys seemed promising for transplant based on the age and health of the donor but were found to have problems that doctors decided made them unsuitable for transplant.

However, some experts believe that as many as half of those discarded kidneys could be transplanted if the system for distributing them better matched the right organ to the proper recipient in a suitable amount of time, The Times reported.

Critics say the current kidney allocation process is inefficient due to issues such as an outdated computer matching program, stifling government oversight, doctors' overreliance on inconclusive tests, and even federal age discrimination laws.

These factors have led to medical rationing system that supposedly gives all transplant candidates a fair chance of receiving a kidney but may not save as many lives as it could.

"There is no doubt that organs that can help somebody and have a survival benefit are being discarded every day," Dr. Dorry Segev, a transplant surgeon at Johns Hopkins University School of Medicine, told The Times.

The current federal system -- which amounts largely to first-come, first-served -- is considered simple and transparent, but many experts contend that it wastes precious opportunities for transplants.

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Six Million Face Health Insurance Tax Penalty: Report

Nearly six million Americans will face a tax penalty under the new health care law for not having health insurance, according to an estimate from the nonpartisan Congressional Budget Office.

The penalty will average about $1,200 per person in 2016, the first year that the penalty is fully in effect, the Associated Press reported.

In an estimate released in 2010 shortly after the new health care law was passed, the budget office estimated that four million people would face a tax penalty for not having insurance.

The law requires that, as of 2014, almost every legal resident of the U.S. must have health insurance or face a tax penalty. There will be exemptions for certain circumstances, including financial hardship and religious objections.

Ninety-eight percent of Americans will not be affected by the tax penalty, Health and Human Services Department spokeswoman Erin Shields Britt told the AP.

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Kroger Spinach Recalled

Packages of Kroger Fresh Selections Tender Spinach sold at grocery stores in 15 states are being recalled due to possible Listeria contamination.

The 10-oz. bags of spinach have a "best if used by" date of Sept. 16 and a universal product code (UPC) of 011110916495, the Associated Press reported.

The Kroger Co. said consumers who bought the spinach should return it to stores for a full refund or replacement.

The recall was announced after a single package of spinach tested positive for Listeria. No illnesses have been reported, the AP said.

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FDA Warns Parents Not to Use Milk Additive

Seven infant deaths have led the U.S. Food and Drug Administration to warn parents not to use SimplyThick, an additive used to thicken infant formula or breast milk.

The product is a thickening gel meant to help premature babies swallow food and keep it down. The seven deaths occurred among 21 premature and one full-term infant who developed inflamed intestines after being given SimplyThick, Bloomberg News reported.

The FDA first warned in May 2011 against giving SimplyThick to premature babies because the product may cause tissue inflammation called necrotizing enterocolitis. On Wednesday, the agency expanded the warning to infants of all ages.

The FDA said further study is needed to determine if there is an actual connection between SimplyThick and necrotizing enterocolitis, Bloomberg reported.